The present invention is used for ATM (Asynchronous Transfer Mode) communication. The present invention relates to a technique of simplifying connection of the internal links of an ATM switch. The present invention also relates to a technique of constituting an ATM switch using an optical device. The present invention also relates to a technique of coping with traffic localization.
FIGS. 16 to 18 explain a conventional ATM switch. FIG. 16 shows the arrangement of a 4.times.4 (m inputs and n outputs are represented by "m.times.n") basic switch. FIG. 17 shows the detailed arrangement of a cross point in the basic switch. FIG. 18 shows the arrangement of a 16.times.16 ATM switch using eight 4.times.4 basic switches. The ATM switch is described in detail in reference "Illustrated standard ATM textbook, ASCII Shuppansha".
The arrangement of the basic switch will be described with reference to FIGS. 16 and 17. An input buffer type basic switch will be described below. This basic switch comprises input buffers 51-1 to 51-4 for temporarily storing arriving cells, a controller 52 for controlling the congestion of cells, cross points 53 for transferring ATM cells output from the input buffers 51-1 to 51-4 to desired output ports, and output highways 54-1 to 54-4 to which ATM cells are transferred. The controller 52 communicates with the respective input buffers 51-1 to 51-4 to permit cell transmission so as not to transfer the cells from the input buffers 51-1 to 51-4 to the same one of the output highways 54-1 to 54-4. The cross point 53 has an address filter AF, as shown in FIG. 17, and transfers an input cell to the corresponding one of the output highways 54-1 to 54-4 on the basis of the information in the header of the cell.
The conventional ATM switch is constituted using a plurality of basic switches shown in FIGS. 16 and 17. FIG. 18 shows a 16.times.16 ATM switch constituted using eight 4.times.4 basic switches 71 to 78. The basic switches 71 to 74 are individually connected to the basic switches 75 to 78 through links so that a cell from an arbitrary input line can be output to an arbitrary output line.
When the ATM switch is to be constituted using a plurality of basic switches, a number of links are required to mutually connect the respective basic switches. In addition, wires for connection are intertwined with each other to result in a complex structure. In the example shown in FIG. 18, 16 links are necessary. An actual large-scale ATM switch uses several ten or several hundred basic switches, and the number of links therebetween is enormous.
The links are constituted using optical fibers. The process of connecting the wires requires a long time. In addition, the check process for preventing erroneous interconnection increases the apparatus cost and the work time. Every time the number of basic switches is increased/decreased, interconnections between the wires must be changed for all the basic switches, so the degree of freedom in increasing/decreasing the number of basic switches is low.
When the traffics localize in routes from the basic switch 71 to the basic switch 75 and from the basic switch 72 to the basic switch 76, the links connecting these switches congest. This situation is shown in FIG. 19. FIG. 19 shows the congestion situation of the 16.times.16 ATM switch. This largely degrades the throughput of the switch.